The global distribution of wrinkle ridges on Venus

New digital mapping of over 65,000 wrinkle ridges of the plains of Venus shows a strong correlation between the location and orientation of these long, low-amplitude compressive anticlines and major features of the geoid and long-wavelength topography. Regions with wrinkle ridges occupy 43 % of the plains and are strongly skewed toward low elevations and negative geoid anomalies. About 93 % of the wrinkle ridge plains lie below mean planetary radius and 72 % have negative geoid anomalies. In contrast, the extensional rift zones of Venus are strongly skewed toward high elevations and positive geoid anomalies. Thus compressive deformation dominates the topographic and geoid lows, whereas extensional rifting is generally restricted to the highs. These observations are consistent with geoid-based stress models that predict compression in geoid lows and extension in geoid highs. The orientations of wrinkle ridges are generally consistent over regions extending for 1000-10,000 km. Many regions have multiple sets of wrinkle ridges of different orientations reflecting multiple episodes and directions of compression; however, about 80 % of the regions display a single dominant wrinkle ridge orientation, with secondary orientations subordinate. The dominant wrinkle ridge orientations in many regions follow the contours of long-wavelength topography and geoid or lie along the axes of troughs in the geoid. Thus the maximum horizontal compression recorded by the folds is commonly parallel to the present-day gradient in geoid and topography, although some regions are strong exceptions, perhaps reflecting changes in topography and geoid with time. The dominant wrinkle ridge trends ring several major geoid and topographic swells, especially Western Aphrodite Terra and Lada Terra, with ring diameters of 75-120 degrees (8000-13,000 Mn). In addition there are smaller rings of wrinkle ridges around the swells in Themis, Eistla, and Bell regiones, especially Gula Mons, with ring diameters of 25-45 degrees (2500-5000 km). In contrast, there are no rings of compressive deformation surrounding some other geoid/topographic highs, including Beta and Atla regiones, which have been proposed to be the youngest swells and display the largest peak geoid/topography ratios and largest geoid gradients. These observations are consistent with the idea that not all the major topographic/geoid swells existed on Venus at the time of wrinkle ridge formation, (C) 1999 Academic Press.